This invention relates to a method of controlling the rate of release of perfumes from continuous action air fresheners and more particularly to controlling the rate of release of perfumes from continuous action air fresheners having cellulosic substrates as the perfume reservoir and generator.
Continuous action air fresheners are slow diffusers which release perfume into an environment at a relatively controlled rate over an extended period of time to impart a desirable perfume to cover or mask undesirable odors which may be present. There have been numerous materials described as reservoirs for continuous action air fresheners. Some of these reservoirs such as carrageenin gels as disclosed in U.S. Pat. No. 2,927,055, metal crosslinked carboxymetyl cellulose gels as disclosed in U.S. Pat. No. 3,969,280 and amylose gels as described in U.S. Pat. No. 4,071,616 inherently release perfume over an extended period of time as the gel evaporates or sublimes into the atmosphere. There also have been attempts to control the release of perfumes from cellulosic substrates such as described in Belgian Pat. No. 865,425 which utilizes specific nonionic surfactants, namely, octyl and nonyl phenols having relatively high degree of ethoxylation and British Pat. No. 1,517,410 which describes the use of polyethylene or another plastic film to surround a cellulosic substrate to control the rate of release of the perfume from the substrate.
The various carrageenin, CMC and amylose gels, although effective as continuous action air fresheners are somewhat difficult to prepare and all have some form of syneresis present in the product. Furthermore, these gels typically have a useful life of 21-30 days. Furthermore, these products are heavy because of the high water content and must be protected from freezing as the gels generally are not freeze-thaw stable.
On the other hand the products using cellulosic substrates as reservoirs and generators as typified by the above-noted Belgian and British patents offer certain advantages over the gel-type forms. However, the structure as exemplied by the above-noted British patent is difficult to package because the plastic or polyethylene film wrapper is permeable to the perfume. When this package is sealed in an outer impermeable package, the perfume diffuses through the inner package to form a damp or wet surface on the film when the package is opened. This can be solved by using various ampoules to contain the perfume, however, this also has some disadvantages. The use of a vapor retardant as taught in the Belgian patent acts to slow down the perfume without requiring artificial barriers and the like. The particular vapor retardants described in this patent do not control the rate of release of the perfume to an acceptable degree for extended product life.
U.S. Pat. No. 3,016,199 contains a general disclosure of the use of nonionic surfactants similar to those taught in the Belgian patent in combination with cellulosic substrates and perfumes.
It has now been discovered, however, that certain surfactants having a particular critical degree of ethoxylation have superior vapor retardant properties as compared to the nonionic surfactants generally disclosed in Belgian Pat. No. 865,425 and U.S. Pat. No. 3,016,199.